Switched mode power supply (SMPS) devices have traditionally been used to supply power in low-power applications, such as computer systems, consumer electronics, et cetera. The advantages of SMPSs are, among others, small size and good efficiency. Therefore, adopting a SMPS for supplying power in an elevator power system is considered.
Traditionally SMPSs have been operable to supply power in one direction only. In elevator power systems, however, bidirectional supply of power is required. When operating in driving mode, elevator hoisting machine retrieves electrical power from elevator power supply (e.g. mains electricity or backup power supply) to drive elevator car along the elevator hoistway. When operating in generator mode, on the other hand, elevator hoisting machine brakes movement of the elevator car and supplies electrical power back to the elevator power supply.
One solution for bidirectional supply of power is to use two separate antiparallel-connected SMPSs to supply power in opposite directions. This means however that more SMPS units are needed, which somewhat voids the small-size advantage and also increases costs and system complexity.
Some bi-directional SMPSs are also known. These however use substantially low switching frequencies where higher impedance of filtering circuitry can be tolerated. Lower switching frequency has the drawback that the size of the device tends to increase.